WO2005108320A2 - Powder particles that are uniformly coated with functional groups, method for their production and use thereof - Google Patents

Abstract

The invention relates to a method for producing powder particles that are uniformly coated with functional groups. According to said method, a suspension of particles of a crude powder is reacted with a coating reagent that contains at least one functional group. The suspension is homogenised in an agitation mill, where the particles are reacted with the coating reagent. The powder thus obtained is suitable for use as a filler in dental materials, cosmetic compositions, pharmaceutical compositions, paints, coatings, rubber mixtures and adhesives.

Description

 Powder particles coated homogeneously with functional groups, a process for their preparation and their use

description

The invention relates to a process for the production of functional groups of homogeneously coated powder particles, in particular glass, glass ceramic and / or ceramic powders, powders thus obtained and their use.

Such powders are widely used in a large area of technology and are obtained by coating a raw powder, for example such powders are used as glass powder, inter alia, in dental technology for the production of filled plastic resins in cosmetic and pharmaceutical formulations. They are also used in paints, varnishes, plasters and wood preservatives both outdoors and indoors as well as fillers in adhesives to increase hardness or reduce elongation. The production of particularly fine-particle powders with small and very small grain sizes is described, for example, in US Pat. No. 6,010,085. In addition, the production of the finest contamination-free (high-purity) glass powder with an average grain size d ₅₀ of 0.2 μm to 10 μm is known from US Pat. No. 5,340,776, ad ₅₀ value of 0.2 μm meaning that 50% of all grains are smaller than 0.2 μm. In this process, a glass powder with a maximum with a particle size of ≤ 300 μm in a stirrer or attritor mill with glass grinding media, the abrasion of which does not impair the properties of the glass powder produced, such as the refractive index. This grinding process is carried out in the presence of a grinding liquid to the desired particle size, then the grinding slip is frozen and then the grinding liquid is removed from the grinding slip by freeze-drying.

If such powders are used as fillers for plastics in dental technology, it is important that the refractive index of the glass powder matches that of the plastic very well in order to achieve high transparency and translucency of the filled plastic. However, if the glass powder contains particles from impurities, such as abrasion from the grinder with different refractive indices, translucency and transparency and possibly the color of the filled plastic deteriorate, so that use is often no longer possible or only to a very limited extent.

For this reason it is described in US Pat. No. 6,010,085 and US Pat. No. 5,340,776 to coat all parts subject to wear, such as the grinding container and the grinding or agitator, with the same material from which the powder is made or with a powder To coat plastic coating, which can be easily removed by extraction, distillation or pyrolysis. In order to achieve better incorporation of the glass powder into the plastic matrix when used as a filler for plastics, the surface of the glass powder particles is usually / frequently coated with suitable silanes. Such a method is described for example in PCT / US92 / 04553. The silanization is usually carried out in such a way that the silane is next dissolved and pre-hydrolyzed with a suitable solvent and then applied to the already ground glass powder, for example in a mixer such as a planetary mixer or in vibration or drum mills. With this procedure, however, the silanes immediately form di-, tri- or also oligomers, which not only form silanol agglomerates, but also aggregates with the remaining silanol groups of already partially coated particles up to a size of 100-300 μm. The formation of these agglomerates or aggregates cannot be prevented with the above-mentioned mixers or mills. Even subsequent grinding of the agglomerates does not lead to usable products.

The aim of the invention is to provide a method which is suitable for coating powder in a homogeneously functional manner without agglomerates being formed or the powder particles being glued to one another by the coating agent (so-called chemical agglomeration).

Another object of the invention is to increase the density of the coating that can be achieved with the methods of the prior art.

This goal is achieved with the method described in claim 1. It has been found that highly pure agglomerate-free and homogeneously coated powders are obtained.

The process according to the invention is preferably carried out in a suspension of the powder in a suspending agent. In principle, the coating reagent can also serve as a suspending agent. According to the invention, however, prefers to use a liquid suspending agent. Both inorganic and organic solvents, such as water or else hydrophilic, hydrophobic, protonic or aprotic organic solvents, can serve as liquid suspending agents. Alcohols or ketones are preferred among the organic solvents. In principle, however, the person skilled in the art selects the suspending agent based on the powder and / or coating reagent used.

The coating reagents used in the method according to the invention have at least one functional group which can form a chemical bond with the powder raw material and / or bind firmly absorptively to the surface of the powder particles. Such groups depend on the powder material used in each case. However, silanol groups are preferably used. Preferred silanols are alkoxysilanes, in particular trialkoxysilanes, such as 3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-aminoethy1-3-aminopropyl-trimethoxysiloxyloxiloxyliloxyliloxyliloxysiloxyliloxysiloxysiloxyloxysiloxyloxysiloxyloxysiloxyloxysiloxyloxysiloxyloxysiloxyloxysiloxyloxysiloxyloxyl , hexadecyltrimethoxysilane, iso-Butyltrime- thoxysilan, iso-butyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane acryloxypropyltriethoxysilane, 3-meth, methyltrimethoxysilane, methyltriethoxysilane Me, octyltrimethoxysilane, silane Octyltriethoxy-, pentyltrimethoxysilane, propyltrimethoxysilane, triethoxysilane product, ( 2-aminoethyl) -2-aminoethyl-3-amino-propyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, tetramethoxysilane, tetraethoxysilane. The coating reagent preferably has a further functional group which, after coating, is available for implementation or reaction with corresponding partners. Such functional groups are, for example, amino, mercapto, acrylic or methacrylic, vinyl, substituted carboxy groups, alkyl groups, in particular Ci to C ₂₀ alkyl groups, alkoxy groups, in particular Ci to C ₂₀ alkoxy groups, the alkyl and the alkoxy groups being straight-chain , branched, cyclic, heterocyclic and / or aromatic and if necessary. Having double bonds, cyano group, isocyano groups, cyanato groups, isocyanato groups, acid anhydrides, in particular cyclic anhydrides such as succinic anhydride, epoxy group such as in particular etoxy groups such as glycidooxy groups, carbamates, etc. Such reactants impart desired properties, such as properties, such as incorporation into a plastic matrix, to the powder surface -Absorption, dirt-repellent properties, improved suspendability, etc.

Both inorganic and organic powders or powder particles can be used in the process according to the invention. However, powder particles made of inorganic material are preferably used. A particularly preferred powder material are inorganic oxidic materials such as Si0 ₂ , Ti0 ₂ and glass, glass ceramic and ceramic-forming materials. The material can be both crystalline, semi-crystalline and amorphous. A particularly preferred powder material is glass, quartz, glass ceramic and ceramic. Preferred solvents and / or suspending agents are water or mixtures of at least 50% by weight water and at least one water-soluble oxygen-containing organic compound with 1 to 5 carbon atoms in the molecule. As orga- African compound are suitable aldehydes, such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, pentanal, ketones such as acetone, methyl ethyl ketone, diethyl ketone, esters, for example ethyl acetate, methyl acetate, propyl acetate, methyl, ethyl, propyl formate or acids, such as acetic acid, propionic acid , Mono-, di- and trihydric alcohols are also suitable. Glycerol, for example, is suitable as the trihydric alcohol and, for example, ethylene glycol or the propanediols are suitable as the dihydric alcohols. The monohydric alcohols are particularly suitable, in particular those with up to five C atoms in the molecule. Mixtures of water with organic compounds are preferred. Particularly preferred are acetone, tert. -Butyl alcohol, methanol, ethanol and n- and i-propanol. Mixtures of these alcohols and acetone with 80 to 99% by weight of water result in particularly good conversion and good homogenization.

The reagent is preferably not added in the prereacted state. In particular, the reagent is not presolvolyzed before it is added and, in particular, is not pre-hydrolyzed.

The suspension used in the process according to the invention preferably has a weight ratio of solvent to powder particles of 0.5: 1 to 5: 1 and in particular of 1: 1 to 4: 1. Particularly preferred ratios are 2: 1 to 4: 1, 1.8: 1 to 4: 1 and in particular 1.9: 1 to 3.5: 1 being very particularly preferred.

The particles used in the process according to the invention are preferably finely divided, sizes d ₅₀ <5 μm, in particular <2 μm, being preferred. Average particle sizes d ₅₀ of <0.4 μm and are particularly preferred in particular <0.2 μm. The particles used in the process according to the invention can be ground directly to the desired size in the attritor or introduced into the desired size. If correspondingly fine starting powders are obtained, then powders with a narrow grain size distribution of 50-400 nm and in particular of 180-220 nm can also be obtained with the attritor mill.

In a preferred embodiment according to the invention, a coated attritor mill is used, as described, for example, in the aforementioned DE-A 41 00 604 or US Pat. No. 6,010,085. A preferred coating material according to the invention is a polymerized resin. A preferred polymerized resin is polyurethane.

According to the invention, the reagent is used in an amount of 0.5-15% by weight, based on the powder mass. Preferred quantity ranges are 1-12% by weight, with 2-10% by weight being particularly preferred. The quantity optimized for the respective purpose also depends on the desired final fineness of the powder and can easily be determined by a person skilled in the art using simple experiments.

After the reaction has ended, the suspension is discharged from the attritor mill and the suspension medium and unreacted reagent are preferably removed by drying. In particular, evaporation of the solvent or suspending agent by heating, if appropriate under vacuum, has proven to be a drying method. Freeze drying is a preferred and expedient method in many cases. In some cases, it is preferred according to the invention to carry out unreacted reagent by means of extraction in a solvent suitable for this. Preferred solvents are those which solvate the reagent to be removed particularly well. In the case of trialkylsilanes, these are especially alcohols. Impurities from plastics, such as resins, in particular polyurethanes, contained in the reaction product due to abrasion can also be removed in the process according to the invention by extraction, such as ether.

It has been shown that particularly fine and highly pure powder particles can be obtained by means of the method according to the invention. In addition, it can be assumed that the coating obtained according to the invention takes place in a monolayer. In addition, the proportion of unbound silane can be reduced dramatically with the method according to the invention in comparison with the methods of the prior art. With the method according to the invention, particularly homogeneously coated powder particles are obtained because agglomerates or aggregates are prevented during the coating.

The invention also relates to coated powder materials themselves, specifically in particular powder materials with a grain size d ₅₀ of <2 μm coated with a monolayer, grain sizes <1.5 μm and in particular <1 μm being particularly preferred. The powder is free of aggregates and agglomerates. Powders with grain sizes d ₅₀ <0.7 μm and <0.4 μm are particularly preferred. Powders with grain sizes <0.2 μm are particularly preferred. Here, d _{50 describes} the average particle diameter, which characterizes the grain size when passing through a sieve, A sieve of the specified size passes 50%, in particular% by weight, of the particles through the mesh, whereas the other 50% do not pass the sieve.

The process according to the invention is carried out as follows:

In a stirrer mill, the desired glass material to be coated is first wet-milled to the desired size, and the reagent is added to the stirrer directly or at any later point in time without prehydrolysis. The reagent is first homogenized in the slip and only gradually hydrolyzed after its homogeneous distribution in the glass powder slip.

The termination of the silanization reaction is indicated by a sharp increase in viscosity, so that it can be assumed that the silanization reaction will end if the viscosity does not change or hardly changes.

After about 1 hour the viscosity increases noticeably. The reaction is complete when the viscosity no longer changes (after about 30 more minutes). The slip is pumped off and dried.

The silane content is determined as a loss of mass after the organic residue has burnt out.

The proportion of non-firmly bonded silane is determined as follows: the powder is washed in isopropanol and then the silane content is determined as described above as a loss of mass after the organic residue has burnt out. The specific surface is determined by means of the BET method according to DIN 66131 (1990) with a Flow Sorb 2300 BET device from Micromeritics. The gas consists of a 70:30 mixture of helium and nitrogen.

Depending on the final fineness to be achieved, the pre-ground glass has a grain size d ₅₀ in the range of 0.9-1.2 μm, 0.6-0.9 μm or 0.2-0.6 μm. The grain size distribution was determined using a Cilas 1064L laser granulometer from Quantachrome. It was measured on the grinding slip. The measuring accuracy is ± 1 / im.

The invention also relates to the use of the particles obtained by the process according to the invention as fillers, in particular for dental materials, such as tooth prostheses or partial dentures, and tooth fillings, for cosmetic and pharmaceutical formulations, such as thickeners and / or preservatives in ointments and pastes, and lipsticks, for use as paints and coatings, such as paints, varnishes, plasters and wood preservatives, both outdoors and indoors, in particular as a UV-absorbing or UV-protective coating, and for use in adhesives, for example to increase hardness or to reduce shrinking and stretching effects and to prevent sedimentation. The invention is illustrated by the following examples.

Examples

example 1

In an embodiment according to the invention, 500 g of an ultrafine glass powder with a grain size of d ₅₀ = 0.7 μm are filled into an agitator mill (types PML V + H, DRAIS GmbH, Germany) as an aqueous slip. After sufficient homogenization of the slip, 4% by weight methacryloxypropyltrimetoxy-silane are slowly added to the slip within 3 to 5 minutes. After approx. 1 hour the viscosity of the slip increases noticeably. After a further 30 minutes, the silanization is complete and the slip is pumped out. After drying the slip, a silanized, agglomerate-free glass powder of high purity results. The silane content determined by loss on ignition was 2.5%. The proportion of unbound silane was 0%. The specific surface area of the silanized powder was 20 m ² / g. An electron micrograph of the powder thus obtained is shown in Fig.l (scaling = 10 microns).

Comparative Example 2

In a mixer, 500 g of an ultrafine glass powder with a grain size of d = ₅ o 0.7 microns with vorhydroly- siertem silane mixed (4 wt .-%). After a wetting time of approx. 2 hours, the mixture is discharged and dried. The silane content determined by loss on ignition was 1.8%. The proportion of unbound silane was 22%. The specific surface area of the silanized powder was 7 m ² / g. An electron micrograph of the powder obtained in this way is shown in FIG. 2 (scaling = 5 μm).

Example 3

In an embodiment according to the invention, 500 g of an ultrafine glass powder with a grain size of d ₅₀ = 1.0 μm are placed in an agitator mill as an aqueous slip. After sufficient homogenization of the slip, 3% by weight of the methacryloxypropyltrimetoxy silane are slowly added to the slip. After approx. 1 hour the viscosity of the slip increases noticeably. After a further 30 minutes, the silanization is complete and the slip is pumped out. After drying the slip, a silanized, agglomerate-free glass powder of high purity results. The silane content determined by loss on ignition was 1.9%. The proportion of unbound silane was 0%. The specific surface area of the silanized powder was 10 m ² / g. An electron micrograph of the powder obtained in this way is shown in FIG. 3 (scaling = 5 μm).

Comparative Example 4

500 g of an ultrafine glass powder with a grain size of d ₅₀ = 1.0 μm are mixed with prehydrolyzed silane 3% by weight in a mixing unit. After a wetting time of approx. 2 hours, the mixture is discharged and dried. The silane content determined by loss on ignition was 1.5%. The proportion of unbound silane was 22%. The specific surface of the silanized powder was 3.2 m ² / g. An electron micrograph of the powder obtained in this way is shown in FIG. 4 (scaling = 5 μm). Example 5

In an embodiment according to the invention, 500 g of an ultrafine glass powder with a grain size of d ₅₀ = 0.4 μm are pasted with water into a slurry in a laboratory agitator mill and filled into the aggregate. After sufficient homogenization of the slip, 9% by weight methacryloxypropyltrimetoxy-silane is slowly added to the slip. After about 1 hour, the viscosity of the slicker increases noticeably. After a further 30 minutes, the silanization is complete and the slip is pumped out. After drying the slip, a silanized, agglomerate-free glass powder of high purity results. The silane content determined by loss on ignition was 5%. The proportion of unbound silane was 0%. The specific surface area of the silanized powder was 40 m ² / g. An electron micrograph of the powder obtained in this way is shown in FIG. 5 (scaling = 10 μm).

Comparative Example 6

In a mixer, 500 g of an ultrafine glass powder with a grain size of d = ₅ o 0.4 microns with vorhydroly- siertem silane (9 wt .-%) were mixed. After a wetting time of approx. 2 hours, the mixture is discharged and dried.

The silane content determined by loss on ignition was 5%. The proportion of unbound silane was 24.5%. The specific surface area of the silanized powder was 10 m ² / g. An electron micrograph of the powder thus obtained is shown in Fig. 6 (scaling = 20 μm).

Claims

Powder particles coated homogeneously with functional groups, a process for their preparation and their use 1. A process for the preparation of powder particles coated homogeneously with functional groups by reacting a suspension of particles of a raw powder with a coating reagent containing at least one functional group, characterized in that the suspension is homogenized in a stirred grinder and the particles are reacted therein with the coating reagent. 2. The method according to claim 1, characterized in that the particles consist of glass, quartz, glass ceramic and / or ceramic. 3. The method according to claim 1, characterized in that the implementation takes place in a coated agitator grinder. 4. The method according to any one of the preceding claims, characterized in that a silane is used as the coating reagent. 5. The method according to any one of the preceding claims, characterized in that the suspension is carried out by means of an aqueous suspending agent. 6. The method according to any one of the preceding claims, characterized in that powder particles with a particle size of d ₅₀ <2 microns are generated. 7. The method according to any one of the preceding claims, characterized in that particles are generated with a specific surface area of 5-40 m / g. 8. The method according to any one of the preceding claims, characterized in that the suspension has a ratio of suspending agent to solid particles of 1: 1 to 5: 1. 9. The method according to any one of the preceding claims, characterized in that the reaction is carried out with a weight ratio of powder to reagent of 1: 0.005 to 1: 0.2. 10. Homogeneously coated powder obtainable by the process of claims 1-9. 11. Use of a powder obtained according to claim 10 or according to one of claims 1-9 as a filler in dental materials, cosmetic compositions, pharmaceutical compositions, powder coatings, paints, coatings, rubber mixtures and in adhesives. * * *